Weird rattle sound that feels like hammering at low idle

[bjorkmae]

I just swapped a 5sp in place of the auto and thats when the problem started. I hear this rattling noise that also feels like hammering. It always occurs during startup or engine shut down. It can occur at idle but won't occur until the engine is really warmed up. It won't occur while driving although if you idle down a hill you can feel it hammer a little bit. I have checked everything and I can't find anything loose and it drives fine. The cat has been replaced before but I did get a cat below efficiency code tonight. I tried shaking the cat but I couldn't really tell if it was making any noise. If I pull on the engine with my hands really hard when this is happening the noise will stop. Could my cat really cause this and be able to feel it while idling down a hill at low speed? Please help!

 

[HondaLuver83]

Check all your motor and transmission mount

 

[bjorkmae]

98 accord ex 4cyl. I didn't swap the rear mount and bracket, although it all bolted up fine. The MTX computer doesn't control the vacuum for the rear mount so I just hooked it up to vacuum all the time last night and it still does it. All mount are visually good. Whats wierd is that it only happens for a second at startup and shut down and when idling only when the car is hot and recently driven within 5 minutes. If I drive the car a few miles it will do it at idle but will stop doing it after a few minutes of just idling. Power is still good. Could the cat really cause this? I crawled under the car last night to check and all mounts are tight, everything is tight and I can barely hear the noise from under the hood but it is much louder inside the car.

 

[HondaLuver83]

If the sound goes away when you pull on the engine, then it has to be something related to holding the engine in place, and or transmission.

You can check ur cat when its cold by hitting it with a rubber mallet to see if u hear any marble sounds. I doubt this happened in coincidence with your swap.

Does your car vibrate bad or anything like that?

 

[JMillerUA6]

Sounds like it could be a loose or rusted heat shield somewhere. I'd slide my *** under the car and check them all out.

 

[changaroo]

did your torque the flywheel bolts down correctly? they could be backing out -.-

 

[bjorkmae]

I think I may have found the problem. I think it really is the rear mount. I pulled 2 plug wires to simulate the vibration so I could have a while to look at it and the sound appears to be from the rear mount. I must have tore it during a launch or something.

 

[bjorkmae]

Ok I replaced the rear atx motor mount and bracket with a mtx one. First of all what a pain in the ***! But the problem is still there and I swear it seams to be getting worse. Cat looks perfect from the outside and still looks new and the rest of the exhaust looks good too including all heat shields.

 

[HondaLuver83]

Ok I replaced the rear atx motor mount and bracket with a mtx one. First of all what a pain in the ***! But the problem is still there and I swear it seams to be getting worse. Cat looks perfect from the outside and still looks new and the rest of the exhaust looks good too including all heat shields.

Your in portland oregon, Why dont we meet up somewhere so i can take a look. Maybe on the weekend or something

 

[bjorkmae]

That might be a good idea! Vibrations, as previously noted, are often hard to diagnose because they can be amplified and sound like they are coming from somewhere else then where they are actually coming from. The part that makes me think it could be the cat is the lack of any evidence of something actually hitting something and the fact that I got a catalyist effeciency below threshold code that I never had before this problem. If memory serves me correctly the car didn't make any noises when I first test drove it after the swap but started making the noises on my way home from my parents place. Maybe I should pull the O2 sensor and put a screw driver into the cat and see if its loose.